Engine overheating help

Discussion in 'Small Block Tech' started by jaye, Mar 31, 2020.

  1. jaye

    jaye Well-Known Member

    Don’t bash me to much, the issue is with a friend’s stock sbc350. When he drives the temperature goes beyond 250 degrees, so he stops to cool down, he said the upper radiator hose is hard and seems to be bulging. We did a cranking pressure test today ranges were Fromm 160-175, average was 155.25. Cylinders #4 & 8 had burnt crust on the spark plugs. All other plugs are look good. Oil and coolant is clean , thermostat is installed correctly. Other than overheating starts and idle good.
     
  2. gsgnnut

    gsgnnut Well-Known Member

    Could be a number of things- wrong timing, plugged radiator toasted fan clutch, no fan shroud improperly set up fan etc. More details on set up needed to proper diagnose
     
  3. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    What year sbc?
     
  4. gsgnnut

    gsgnnut Well-Known Member

    Sbc usually run super cool 160-180 when set up properly.
     
  5. gsgnnut

    gsgnnut Well-Known Member

    A spent fan clutch will hit 230- 250 fairly quick as will a clogged rad
     
  6. jaye

    jaye Well-Known Member

    It’s on a 64 impala , I don’t know timing. Everything look original, I was thinking clutch fan but that would not account for the top hose getting hard, radiator has a shroud however it look to be the original copper one which could be clogged.
     
  7. alec296

    alec296 i need another buick

    Heat builds pressure. Radiator is probably plugged.
     
  8. Fox's Den

    Fox's Den 355Xrs

    yep what they said^^
     
  9. jaye

    jaye Well-Known Member

    Thanks for the insights and opinions.
     
  10. 455monte

    455monte Well-Known Member

    What belt drive system is on it?
    Original v belts or serpentine belt?
    Serp belt uses a reverse flow water pump.
    Will heat up fairly fast when wrong pump is used.
    Or if pumps been on there for a long time the impeller wheel fins could be rotted and not moving correct volume of coolant.
     
  11. pbr400

    pbr400 68GS400

    Unless he’s been vigilant about using antifreeze and distilled water (not tap water) I vote clogged radiator, too.
    Patrick
     
  12. alec296

    alec296 i need another buick

    The reverse water pump can be an issue if it has that. Keeps hot coolant away from thermostat. Gets hot on gauge but engine isn’t really really hot. By now getting as hot as your saying would have done some damage by now.
     
    Last edited: Apr 1, 2020
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Overheats when? On highway? Does it cool down during stop and go?
     
  14. RIVI1379

    RIVI1379 Well-Known Member

    Does a 64 even have a clutch for the fan?...not that it couldn’t my bow tie knowledge is limited but it would seem possibly not? Another opportunity to learn. But as been said SBC do normally run real cool, and just by design that car would seem to get plenty of air over the rad surface - if I’m reading this right it’s hearing at speed and not at stops ? Which would seem to be a lack of flow or something impeding airflow while its under load...like a bad clutch but I’m not sure it would have to even have one.
     
  15. BadBrad

    BadBrad Got 4-speed?

    Does it have a functioning vacuum advance? Inoperative VA will cause this problem.
     
  16. Stevem

    Stevem Well-Known Member

    If it can idle and cool down then it's more then likely a coolant flow issue, like the Rad is restricted or the water pump impellers have worn.

    Also confirm that the vacuum advance is working at part throttle hiway speeds as I have seen failure of that add 15 degrees of coolant temp to a motor, and retarded timing from a worn timing chain will do the same thing even though a compression test may show decent numbers.
    To check pull out all the plugs, pop off the Dizzy cap and hand Crank the motor from the Balancer back and forth and see how closely the Dizzy rotor follows the Crank movement.
     
    Last edited: Apr 2, 2020
  17. 72skylarkconvt

    72skylarkconvt Well-Known Member

    Rad may clogged or the clutch fan (assuming it has one) is shot. Does it stay cool driving around back roads (25mph or so?) but when on the hwy it starts heating up real bad? If so the rad is prob clogged, not allowing enough airflow through it. Once off HWY is it hard to get to cool down? May be the clutch fan then if it has one. Those in the end were my overheating issues.
     
  18. jaye

    jaye Well-Known Member

    I was thinking VA also when you plug/unplug the vac line the engine idle doesn’t change. We changed the radiator and water pump started out good power on acceleration temp 190. Left the store to return home temp went up power decreased like car didn’t want to move. Pulled over let it sit a few hours started right up and drove home no problem.
     
  19. alec296

    alec296 i need another buick

    Try a different gas cap. Venting may plugged.
     

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